The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected data tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in limited area and volume. A technical approach to meeting this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
Magnetoresistive effect type magnetic heads are employed as sensors for reading magnetic information (data) recorded on a magnetic recording medium (such as a hard disk) in high-density magnetic recording devices (such as HDDs). The use of magnetic read heads that utilize a magnetoresistive effect has become commonplace. One such magnetoresistive effect type read head uses a giant magnetoresistive (GMR) effect in a multi-layered film formed by laminating a ferromagnetic metal layer on a non-magnetic intermediate layer. The first kind of GMR heads employed were Current-In-Plane (CPP)-type heads in which electrical signals flow in parallel with the film plane to the sensor membrane. Next, Tunneling Magnetoresistive (TMR)-effect heads and Current-Perpendicular-To-Plane (CPP)-GMR heads, which are considered advantageous from the standpoint of track narrowing, gap narrowing, and increased output, were developed with improved recording density in mind.
While the demand in recent years for even higher density recording has been met by techniques based on narrowing the effective track width of a magnetoresistive sensor, this track width narrowing has resulted in other problems of increased element resistance, increased electrical and magnetic noise, and as a result, lowered sensitivity and difficulties in increasing the sensitivity.
Multi-sensor reader structures designed to accommodate higher density recording have been proposed to alleviate these problems. Multi-sensor readers are advantageous in that they allow for a magnetic head with a large number of sensors of a size greater than a bit size of the medium, and this allows for bit data to be read from the difference in the plurality of signals produced thereby. Because the sensor size may be increased beyond a single bit size, noise may be suppressed and sensitivity may be increased. However, multi-sensor readers that have staggered or offset sensors that are positioned above or below other sensors encounter a unique problem when reading data on the inside or outside tracks of a HDD.
When reading data from a target track using a three sensor reader structure, with a lower sensor positioned below and between two upper sensors, the lower sensor will be positioned on the target track, with the two upper sensors positioned across the target track and neighboring tracks. This is sometimes referred to as a multiple input multiple output (MIMO) configuration. Each sensor reads multiple signals from the target track and neighboring tracks at the same time, then only target track signal information is extracted using a signal-processing algorithm. This allows for sensors that are wider than a track width to be used, while still keeping a high read sensitivity.
When reading data from outer tracks (OD) or inner tracks (ID) of a magnetic disk, the magnetic head having the multi-sensor reader structure is rotated by a skew angle, which causes at least one of the upper sensors to be shifted to an adjacent track, thereby introducing error into the data signal read from the magnetic disk. In the case of a conventional MIMO head, when the lower sensor is aligned to the target track, a distance between the lower sensor and the upper sensors causes one of the upper sensors to depart from the target track because of the skew angle.